In an air-conditioning apparatus, a method of driving a motor used for a compressor, a fan, and the like with an inverter for the purpose of energy saving has become mainstream. According to this method, first, an alternating current is converted by a converter to a direct current, and the direct current is converted by the inverter to an alternating current having an optional voltage and frequency. By using the alternating current having the optional voltage and frequency, the motor is driven, whereby it is possible to operate the motor with high efficiency. In recent years, an air-conditioning apparatus has been proposed in which, in pursuit of further energy saving, a boosting circuit is provided at the input side of an inverter, a rectification output rectified by a converter is boosted by using the boosting circuit, and the boosted rectification output is inputted to the inverter.
In general, in a converter, a temperature detection unit such as a thermistor is provided near a semiconductor element used as a switching element, and a result of detection at the temperature detection unit is monitored to suppress abnormal superheating of the semiconductor element. Furthermore, a technique has also been proposed in which, in addition to the result of detection at the temperature detection unit, information such as an operation pattern is monitored to suppress abnormal superheating of the semiconductor element.
Patent Literature 1 discloses an inverter device which includes: a voltage detection circuit which detects an input voltage of a converter circuit; and a temperature detector which detects a temperature near the converter circuit. Patent Literature 1 is intended to control an inverter circuit on the basis of the relationship between the input voltage detected by the voltage detection circuit and the temperature detected by the temperature detector, to suppress an increase in the temperature of a switching element of the converter circuit.
Patent Literature 2 discloses a controller including a temperature estimation unit which estimates the temperature of an inverter on the basis of information regarding an operating state of the inverter. Patent Literature 2 is intended to provide an upper limit for the operating voltage of the inverter on the basis of the temperature of the inverter estimated by the temperature estimation unit, to prevent a voltage exceeding the withstand voltage of the switching element of the inverter from being applied to the inverter.